Science Objectives for Everyone
The Binary Colloidal Alloy Test 5: Three-Dimensional Melt (BCAT-5-3D-Melt) experiment crystallizes and melts tiny particles suspended in liquids, known as colloids, onboard the International Space Station where there is no gravity. The colloidal particles are designed to melt when the temperature of the liquid is raised. Crewmembers observe and photograph the particles as their sizes change when subjected to small temperature adjustments.

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The following content was provided by Arjun Yodh, Ph.D., and is maintained in a database by the ISS Program Science Office.

Experiment Details

OpNom: BCAT-5

Principal Investigator(s)
Arjun Yodh, Ph.D., University of Pennsylvania, Philadelphia, PA, United States

The Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3D-Melt) takes advantage of the microgravity environment on the ISS to allow the liquid suspended particles to crystallize and melt without the interference of gravitational forces which can alter the nature of these processes.

The particles are designed to melt when temperatures warm above 23

Description
The Binary Colloidal Alloy Test - 5 (BCAT-5) hardware supports four investigations. Samples 1 - 5, the Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) will study collapse (phase separation rates that impact product shelf-life). In microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth. Samples 6 - 8, Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) will study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials. Sample 9, Binary Colloidal Alloy Test - 5: Seeded Growth (BCAT-5-SeededGrowth) will study the properties of concentrated systems of small particles when 99.8% are identical 0.36 diameter micron spheres and 0.2% are 4.14 microns in diameter (11.5x larger); these seed particles may cause heterogeneous crystal growth. Sample 10, Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3D-Melt) will look at the mechanisms of crystal formation and 3-dimensional melting using colloidal particles that change size with temperature.

The BCAT-5-3D-Melt sample will consist of a monodisperse nearly-hard-sphere colloidal suspension near its crystallization point. For this investigation small temperature changes that change the particle volume fraction will move the equilibrium system towards and away from the melting transition. The key ingredient in these samples is a thermosensitive polymer, poly(N-isopropylacrylamide (NIPA); the temperature-sensitive character of the samples stems from the temperature dependent solubility of NIPA polymer in water. Below its theta temperature (the temperature at which the coiled polymer molecules expand to their full contour lengths and become rod-shaped) of approximately 31 degrees C, water is a good solvent and NIPA polymer assumes a swollen coil form; in this regime a small increase of temperature increases monomer-monomer attractions and thus the size of the isolated polymer decreases. Above the theta temperature, water is a poor solvent and NIPA has a collapsed globule form.

The BCAT-5-3D-Melt experiment will simply record sample temperature and observe (by photography) whether the sample crystallizes, noting at what temperature the sample experiences the fluid-solid transition. This information will be also be useful for future experiments planned for ISS.

Space Applications
The BCAT experiments can only take place in a microgravity environment, because gravitational forces alter the nature of the crystallization and melting processes. BCAT-5 gives scientists insight into how the size of particles affects their ability to organize into crystal structures. A better understanding of this phenomenon could lead to manufacturing improved materials and products for space applications.

Operational Requirements
The BCAT-5 experiment consists of ten small samples of colloidal particles. The ten BCAT-5 samples are contained within a small case the size of a school textbook. The experiment requires a crewmember to set up on the Maintenance Work Area (MWA) or on a handrail/seat track configuration. Initially the sample will require manual photographs to be downlinked by an astronaut to investigators on the ground for analysis. Following configuration confirmation from investigators the automated EarthKAM software will be setup to take digital photographs of samples at close range using the onboard Kodak DCS760 camera. Camera Control Files for running the EarthKAM software can be uploaded from Earth to control the photography intervals (how many photographs per hour and for how many days) once it is running. The pictures are downlinked to investigators on the ground for analysis.

Operational Protocols
A crewmember sets up the video camera and BCAT-5 hardware (Slow Growth Sample Module, DCS760 Camera, pen-light source, flash and SSC Laptop with EarthKAM software) in the Maintenance Work Area (MWA) to document the BCAT-5 operations as performed on-board the ISS. The crewmember homogenizes (mixes) the sample(s) and takes the first photographs manually. This helps them optimize the setup and shows that the samples were initially fully homogenized when publishing results later. The EarthKAM software automates the rest of the photography session over a period of days to a few weeks. The crewmember performs a daily status check once a day (when time is available) to assure proper alignment and focus. At the completion of the run, the crewmember tears down and stows all hardware.

NASA Image: ISS016E027863 - Astronaut Dan Tani photographing the BCAT-3 Sample Module using his own design for a ceiling mount in Node 2 of the International Space Station. Great high contrast pictures of difficult-to-capture images resulted from using this setup (February 2008).